1. Field of the Invention
The present invention relates to a wire saw. More particularly, it relates to a differential type rotational wire saw having a wire supplied from a wire feeding unit, suspended by movable and fixed rollers in an area upstream and an area downstream and wound around a group of rolls, at least one of which is driven. The wire is gradually moved to a wire withdrawing unit by a reciprocal movement of the wire over the group of rolls caused by the approach or separation movements of the movable rollers with regard to the position of the fixed rollers.
2. Description of the Related Art
The above-mentioned type of the wire saw is disclosed in Japanese Examined Patent Publication (Kokoku) NO. 56-198 and NO. 56-199.
The wire saw disclosed in these publications has the following constitution. Namely in an area upstream and an area downstream of a group of rolls having the wire wound therearound, a set of a plurality of fixed rollers aligned on the same axis as the former group of rolls is arranged at the right side and left sides of a frame of the wire saw, and a swing lever, the center of which is supported at a position lower that a position midway between the fixed rollers on the right side and the fixed rollers on the left side, is provided, and a plurality of movable rollers aligned on the same axis as the group of rollers is arranged at both ends of the swing lever. The wire is wound around the fixed rollers and the movable rollers, and an approaching movement i.e., toward the fixed roller, and a separating movement i.e., away from the fixed roller of the movable roller on the swing lever are applied by movement of the swing lever, to simultaneously generate a slackness in the wire and to absorb the slackness generated upstream and downstream of the roll group, and the wire is then gradually advanced to a withdrawing roller by reciprocal movement of the roll group.
However, this wire saw has a problem in that the wire is easily broken during the advancing movement by the reciprocal movement thereof, and it appears that this breakage of the wire is caused by an irregular tension of the wire. Namely, the movable rollers on the swing lever are moved in a circular locus by the movement of the swing lever. Therefore, when the movable rollers approach the fixed rollers or move away from the fixed rollers along the circular locus, the speed of the movable rollers arranged on the one end of the swing lever and approaching the fixed roller is slightly different to the speed of the movable rollers arranged on the other end of the swing lever and moving away from the fixed roller during the swinging motion of the swing lever.
When there is the difference between the speed of the rollers approaching the fixed rollers and the speed of the rollers moving away from the fixed rollers, a difference in the amount of slack caused in the wire and the amount of take up of that slack is caused by the above-mentioned speed difference. Also, since the wire is wound around several turns on both sets of rollers, the difference between the amount of slack and the amount of take up cause an irregular tension in the wire.
Further, since the swinging movement of the swing lever is performed independently from the operations of the wire supplying unit and the wire withdrawing unit, even if the roll group is driven in synchronism with the swinging movement of the swing lever, the irregularity of the tension of the wire is worsened, so that the wire will be broken the excess load applied to the wire.